Epigenetics is inheritable information not encoded in DNA manifested through control of gene expression, thereby controlling a range of cellular activity, including determining cell fate, stem cell fate and regulating proliferation. Epigenetic control over gene expression is accomplished in at least four ways: (1) covalent histone modification, (2) covalent DNA modification, (3) histone variation, and (4) nucleosome structure and DNA/histone contact points. Epigenetic control through one mechanism can influence the other suggesting a combinatorial regulation, as evidenced by the methylation of histones being implicated in the modulation of DNA methylation.
Covalent histone modifications, a key mechanism involved in epigenetic control, include: (1) lysine acetylation, (2) lysine and arginine methylation, (3) serine and threonine phosphorylation, (4) ADP-ribosylation, (5) ubiquitination, and (6) SUMOylation. Specific enzymatic activities are associated with these modifications and in the case of histone methylation, methyltransferases catalyze the transfer of a methyl group from cofactor S-adenosylmethionine to a lysine or arginine, producing S-adenosylhomocysteine as a by-product. Methyltransferases can also modify residues in other cellular proteins, e.g. the tumor suppressor p53.
Histone methyltransferases fall into subgroups that include arginine methyltransferases, SET-domain containing methyltransferases SU(VAR)3-9, E(Z) and TRX, and DOT-like methyltransferase hDOT1L. Families of SET-domain containing methyltransferases have been identified and include SUV39, SET1, SET2 and RIZ.
The disruption of the normal functions of methyltransferases has been implicated in human diseases. Members of different classes of methyltransferases are implicated in cancer and representative examples for the subgroups and subclasses are provided: (1) hDOT1L, a member of the DOT-like methyltransferases, is linked to leukemogenesis [Nature Cell Biology, 8:1017-1028 (2006); Cell, 121:167-178 (2005); Cell, 112:771-723 (2003)]. (2) EZH2, a SET1 methyltransferase, is up-regulated in tumor cell lines and has been linked to breast, gastric and prostate cancers [British Journal of Cancer, 90:761-769 (2004)]. (3) SUV39-1/2, SUV39 methyltransferases, have been linked to signaling pathways regulating cancer cell growth and differentiation [Genetica, 117(2-3):149-58 (2003)]. (4) NSD1, a SET2 subclass methyltransferase, has been linked to acute myeloid leukemia and Sotos syndrome, a predisposition to cancer [Molecular Cell Biology, 24(12):5184-96 (2004)]. (5) EVI1, a RIZ methyltransferase, is overexpressed in solid tumors and leukemia [Proceeding of the National Academy of Sciences, 93:1642-1647 (1996)]. (6) Related enzymes, namely SMYD2, are lysine methyltransferases that modify the tumor suppressor protein, p53 and through this activity, may function as an oncogene that interferes with p53's protective functions [Nature, 444(7119):629-632 (2006)]. (7) SMYD3, a SET-domain containing lysine methyltransferase, is involved in cancer cell proliferation [Nature Cell Biology, 6(8):731-740 (2004)]. (8) CARM1, an arginine methlytransferase, is linked to prostate cancer [Prostate, 66(12):1292-301 (2006)].
Inappropriate methyltransferase activities thus represent attractive targets for therapeutic intervention by small molecule inhibitors. In fact, inhibitors of SUV(AR) histone methyltransferase [Nature Chemical Biology, 1:143-145 (2005)] and protein arginine methyltransferase [Journal of Biological Chemistry, 279:23892-23899 (2004)] have been described. The present invention relates to novel synthetic compounds effective as inhibitors of inappropriate histone methyltransferase activities that would be useful in treating human diseases, such as cancer.